/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hdfs.protocol;

import java.io.IOException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hdfs.DFSConfigKeys;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenIdentifier;
import org.apache.hadoop.hdfs.security.token.block.BlockTokenSelector;
import org.apache.hadoop.ipc.VersionedProtocol;
import org.apache.hadoop.security.KerberosInfo;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.security.token.TokenInfo;

/**
 * An client-datanode protocol for block recovery
 */
@KerberosInfo(serverPrincipal = DFSConfigKeys.DFS_DATANODE_USER_NAME_KEY)
@TokenInfo(BlockTokenSelector.class)
/*
 * Client与DataNode间的接口
 */
public interface ClientDatanodeProtocol extends VersionedProtocol {
	public static final Log LOG = LogFactory.getLog(ClientDatanodeProtocol.class);

	/**
	 * 4: never return null and always return a newly generated access token
	 */
	public static final long versionID = 4L;

	/**
	 * Start generation-stamp recovery for specified block
	 * 
	 * @param block
	 *            the specified block
	 * @param keepLength
	 *            keep the block length
	 * @param targets
	 *            the list of possible locations of specified block
	 * @return either a new generation stamp, or the original generation stamp.
	 *         Regardless of whether a new generation stamp is returned, a newly
	 *         generated access token is returned as part of the return value.
	 * @throws IOException
	 */
	LocatedBlock recoverBlock(Block block, boolean keepLength, DatanodeInfo[] targets) throws IOException;

	/**
	 * Returns a block object that contains the specified block object from the
	 * specified Datanode.
	 * 
	 * @param block
	 *            the specified block
	 * @return the Block object from the specified Datanode
	 * @throws IOException
	 *             if the block does not exist
	 */
	Block getBlockInfo(Block block) throws IOException;

	/**
	 * Retrieves the path names of the block file and metadata file stored on
	 * the local file system.
	 * 
	 * In order for this method to work, one of the following should be
	 * satisfied:
	 * <ul>
	 * <li>
	 * The client user must be configured at the datanode to be able to use this
	 * method.</li>
	 * <li>
	 * When security is enabled, kerberos authentication must be used to connect
	 * to the datanode.</li>
	 * </ul>
	 * 
	 * @param block
	 *            the specified block on the local datanode
	 * @param token
	 *            the block access token.
	 * @return the BlockLocalPathInfo of a block
	 * @throws IOException
	 *             on error
	 */
	BlockLocalPathInfo getBlockLocalPathInfo(Block block, Token<BlockTokenIdentifier> token) throws IOException;
}
